Efficiency:

The Wild Pyromancer (WP) has 2.5 mana value in basic minion stats and an additional 0.5 mana value from every enemy minion its effect hits and -0.5 mana value for every friendly minion its effect hits. Therefore, YD can have a very high mana efficiency.

Uses and Tactics:

The WP can be used with Equality to destroy all enemy minions (except those with Divine Shield). Unfortunately, this combo will also kill the WP. This combo is also cheaper than the Equality, Consecration combo.

The WP is a great unit to use to activate your own Enrage minions. However, be careful about using the WP when you may Enrage an enemy unit.

The Coin counts as a Spell. This can be used to secure board control early in the game.